It has previously been proposed to construct differentials which can be manually locked; such locking-type differentials, then, will drive both wheels on a common axle at the same speed so that slippage of one wheel, for example on an icy or otherwise slippery surface, will not prevent traction from being applied to the other wheel on the same axle. It is also known to control the torque applied by the engine of the vehicle to the wheels such that, upon acceleration, the wheels will not slip or spin. Frequently, dual control can be used, in which, upon spinning of one wheel, a brake is applied to the spinning wheel, thereby applying additional torque to the other wheel on the axle, connected to the braked wheel by a differential; it is also known to lower the torque applied to the wheels, upon spinning of one or both of the wheels--see, for example, German Pat. No. 3,127,301 to which British No. 2,109,882 corresponds.